Optical telecommunications is a primary method of transporting information around the world. Wavelength Division Multiplexing (WDM) technology has led to as many as 80 and 160 information-carrying wavelengths on a single fiber at bit rates as high as 10 and 40 gigabits per second per wavelength. While this increase in throughput and capacity is impressive, security is becoming increasingly important as the use of fiber optic WDM and free space optical telecommunication systems continue to expand.
Most existing methods of protecting an optical transmission encrypt a signal in the electrical domain before the signal is transferred to the optical layer. For example, in van Breeman et al, U.S. Pat. No. 5,473,696, the data stream is enciphered by adding, modulo 2, a pseudorandom stream before transmission and recovering the data by addition of the same pseudorandom stream. Rutledge, U.S. Pat. No. 5,864,625, electronically encrypts the information and optically transmits a security key used for the encryption process. These types of protection systems are limited by the electronic processing rate, currently, no better than approximately 2.5 to 10 gigabits per second. Secondly, these electronic methods of protection are costly to implement and can create latency issues.
Brackett et al in U.S. Pat. No. 4,866,699 teaches an analog method of coding and decoding for multi-user communications based on optical frequency domain coding and decoding of coherently related spectral components. Brackett fails to address any secure or privacy communication applications where the spectral components are not coherently related.
In view of the foregoing, one object in accordance with the present invention is to improve optical communications security by providing an analog method of protecting transmissions that is lower in cost, volume, weight and/or power, especially at high transmission bit rates.